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SUMMARY
The metabolism of radioactive iodine in the adult male garden lizard, Calotes versicolor, was studied during the course of a year by examination of the following indices of thyroid function: thyroidal 131I uptake, quantitative estimation of labelled iodoamino acids in the thyroid gland and in plasma, and plasma protein-bound iodine. Labelled monoiodotyrosine, di-iodotyrosine and thyroxine were identified and seasonal variations in their proportions demonstrated. Thyroxine was not detected in winter but made its appearance in the spring and summer months. Tri-iodothyronine was not detected at any time of the year in the thyroid of Calotes.
The effects of administration of thyrotrophin (TSH), lowered temperature and dehydration were also studied. TSH augmented 131I incorporation into the thyroid gland significantly but was not effective in stimulating hormonogenesis in winter. While water withdrawal had no effect on thyroidal radioactive iodine uptake, temperature lowered artificially (15 °C) in summer reduced it by half, and altered greatly the proportions of iodoamino acids in the thyroid. The results are discussed in the light of the fragmentary information concerning thyroid function in reptiles.
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Department of Zoology, Banaras Hindu University, Varanasi 221005, India
(Received 16 September 1974)
Almost all birds investigated so far have been shown to respond to artificial illumination irrespective of their tropical or temperate distribution (see reviews Chandola, Thapliyal & Murty, 1973; Follett, 1973; Lofts & Lam, 1973) with the exception of a subtropical finch, spotted munia, Lonchura punctulata (Chandola & Thapliyal, 1973). We have now undertaken a systematic investigation of the photoresponses of this bird which is widely distributed in the Indian subcontinent (16–30° N) and report our preliminary findings here.
Adult birds were caught in the wild and, after an acclimatization period of 15 days, were weighed and the gonads inspected at laparotomy. Male birds were separated into groups of 12 and subjected to light treatments as indicated in Tables 1 and 2. In one series 3 h light: 23 h darkness (3 L: 23 D), an ahemeral light
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Seasonal changes in the thyroid gland related to temperature and reproductive cycles have been observed in a number of reptiles. However, while the temperaturedependence of the thyroid has been well established, experimental studies aimed to demonstrate a direct association between reproductive events and thyroid secretions have so far been lacking (see reviews by Dodd & Matty, 1964; Lynn, 1970). We have now obtained data indicating that male hormone(s) may be of great importance in the maintenance of thyroidal function in lizards.
Indian garden lizards (Calotes versicolor) were housed in a temperature (31 ± 1 °C and photoperiod (12 h light) controlled chamber. Live maggots and water were provided ad libitum. In June, 15 adult males were castrated and 10 were sham-operated under sodium pentobarbitone anaesthesia. After 5 weeks each animal received i.p. 10 μCi carrier-free 131I in 0·2 ml 0·9% NaCl solution. Four to five animals from each group
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SUMMARY
Thyroidectomy and orchidectomy led to significant reduction in the oxidative metabolism of isolated liver and skeletal muscle tissue (at 30 °C) in Calotes versicolor. Thyroxine and male hormone were shown to increase this parameter in intact and orchidectomized lizards respectively. The effects of thyroidectomy and orchidectomy on tissue oxygen uptake were not additive. It is supposed that by its effect on oxidative metabolism male hormone may be of a greater physiological importance for reptiles than for other vertebrates.
The present results show also that changes in environmental temperature can counteract the depressive effect of orchidectomy on the thyroid of this species of lizard.
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SUMMARY
Orchidectomy in Hemidactylus flaviviridis led to significant reduction of thyroidal 131I uptake, thyroidal content of thyroxine, plasma protein-bound iodine and oxygen consumption of isolated liver and skeletal muscle (at 30 °C). Administration of testosterone to orchidectomized lizards restored these parameters to normal levels. Dependence of thyroid function and oxidative metabolism on male hormone may be a general feature in reptiles. This hormone may, therefore, be of greater physiological importance in these animals than in other vertebrates. Since reptiles occupy a crucial phylogenetic position in the animal kingdom these findings are important from the point of view of evolution of the functional aspects of hormones in vertebrates.
The results also show that thyroid function is inhibited by oestrogen(s) in this lizard. This may be an adaptive compensatory measure to control (through effects of the thyroid on metabolic activities) the extra expenditure of energy usually associated with such energy-consuming functions as ovulation and egg-laying.
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Department of Zoology, Banaras Hindu University, Varanasi 221005, India
(Received 18 June 1974)
Male hormone has been classically attributed a primary role in the maintenance of reproductive function in male vertebrates. Thyroid hormone on the other hand has been shown to control oxidative metabolism in homeotherms, but its role in poikilothermous animals has not been established, except in reptiles (see reviews by Dodd & Matty, 1964; Lynn, 1970). Recently oxidative metabolism was shown to be influenced by testosterone in three species of reptiles, namely, Calotes versicolor (Chandola, Kumar & Thapliyal, 1974a), Natrix piscator (Thapliyal, Kumar & Garg, 1974) and Hemidactylus flaviviridis (Chandola et al. 1974b). Castration in all these species resulted in a significant decrease and administration of testosterone in a significant increase in the oxygen consumption of isolated liver and skeletal muscle tissues (at 30 °C). Testosterone also restored the decline in oxygen consumption in castrated animals to normal
